The invention relates to the verification of the operation of a power train with which a motor vehicle is equipped, and in particular the verification of the operation of the sensors embedded in the power train, and the power trains provided with permanent magnet machines.
In the motor vehicles with electric drive, the torque supplied by an electric motor has to be monitored. Since the torque of an electric machine is directly linked to the current flowing therein, these currents have to be controlled with precision.
In a synchronous machine, notably a three-phase permanent magnet synchronous machine with axial flux, the currents flowing in the three phases of the stator are sinusoidal and each phase-shifted by
            2      ⁢                          ⁢      π        3    ⁢          ⁢      rad    .  These currents create a revolving magnetic field in the electric machine. The rotor is made up of a permanent magnet, for example provided with five pairs of poles. Like a compass, the rotor is naturally aligned on the revolving magnetic field created by the stator. Thus, the rotation frequency of the rotor is equal to the frequency of the stator currents. It is the amplitudes of the stator currents and the power of the rotor magnets which create the torque necessary to the rotation of the machine. To control these currents, sinusoidal voltages each equally phase-shifted by
            2      ⁢                          ⁢      π        3    ⁢          ⁢  radtherefore have to be applied to each phase of the stator.
Generally, it is simpler to apply a regulation to constants than to sinusoidal signals. The Park transform is generally used to project a three-phase system onto a two-dimensional space to obtain an equivalent revolving reference frame. It is thus possible to transpose the three currents and the three sinusoidal voltages of the stator relative to the three phases of a three-phase system into a space where the sinusoidal signals are expressed in the form of constant signals (one component on the direct axis d and one component on the quadrature axis q). In the case of a synchronous machine, the Park reference frame is linked to the rotor.
By working with currents and voltages expressed in the Park space, it is thus possible to act on constant currents and voltages rather than on sinusoidal signals to regulate the three-phase machine to be controlled. By doing the inverse transform, it is possible to revert to the normal reference frame of the machine and therefore know exactly what voltages or what currents to apply to each phase of the machine.
Current sensors are generally used to implement a regulation of the torque. It is also possible for sensors suitable for measuring the torque to be used.
As will be understood, a failure of one of the sensors prevents the correct regulation of the torque which has to be supplied by the electric machine. It is therefore necessary to detect such a failure.
Reference will be able to be made to the document JP 2001268980 which describes an estimation of the current flowing in a direct current machine, but this solution is not suited to the machines that operate with sinusoidal currents.
The document U.S. Pat. No. 5,047,699 also describes an estimation of the current flowing in a direct current machine.
The document US 20020008492 describes a detection of the failure of sensors in which the variations of the measurements supplied by the sensors are monitored.